Greenland's ice sheet could disappear within the next 1,000 years if global warming continues at its present rate, a report in Nature magazine suggests.

Jonathan Gregory and colleagues from the University of Reading, UK, say their studies forecast an 8C increase in Greenland's temperature by 2350.

They believe that if the ice cap melts, global average sea level will rise by about 7m (23ft).

Even if global warming was halted the rise could be irreversible, they say.

Warming threshold

The researchers estimated that Greenland was likely to pass a threshold of warming beyond which the ice sheet - second in size to Antarctica - could not be sustained unless much greater reductions were made in emissions of greenhouse gases.

They found that over the next 350 years global warming was likely to pass the critical threshold in 34 out of 35 model calculations.

It's quite possible that Greenland is already making a slight
contribution to global sea levels

Dr Jonathan Gregory, University of Reading

Greenland's average temperature only needs to increase by 3C to melt its ice sheet, but some of the modelling studies forecast a much higher rise by the year 2350.

"Without the ice sheet, the climate of Greenland would be greatly altered," says Dr Gregory.

If the ice sheet was removed, Greenland would be a lot warmer because the land surface would be at a lower altitude and reflect less sunlight.

"Unlike the ice on the Arctic Ocean, much of which melts and reforms each year, the Greenland ice sheet might not re-grow even if the global climate were returned to pre-industrial conditions," he says.

Tentative evidence suggests the ice sheet has already to started to melt.